Characterization of transition joints of commercially pure titanium to 304 stainless steel

Solid-state direct bonding between commercially pure titanium and type 304 austenitic stainless steel has been carried out in the temperature range of 850–950 °C, under a uniaxial pressure of 3 MPa for 1 h. The diffusion bonds have been evaluated using light microscopy, electron probe microanalysis (EPMA), X-ray diffraction (XRD) technique and tensile testing. Light microscopy shows that different intermediate layers are formed in the reaction zone, and the width of these layers increases with an increase in bonding temperature. EPMA revealed that, at any particular bonding temperature, Ti traverses a minimum distance in the 304 stainless steel side, whereas Fe, Cr and Ni travel comparatively larger distances in the Ti side. This microanalysis also indicated different step formations in the concentration profile of Ti, Fe and Cr over different composition ranges in the diffusion zone indicating formation of intermetallic phases that were detected by XRD. Brittle intermetallic phases lower the strength and ductility of the diffusion bonded couples significantly. Best room temperature tensile strength, ∼217 MPa, has been obtained at 850 °C processing temperature due to minimal deleterious effects.